This invention relates to a novel polyester tackifier, adhesive compositions comprising the tackifier and methods of preparation. More specifically, the polyester tackifier is obtainable by polymerising a mixture comprising a diacid or derivative thereof, a diol, and at least 6 molar % of an organic monofunctional compound, wherein the mixture is essentially free from compounds comprising more than two carboxylic acid groups or alcohol groups.
Synthetic polymers such as acrylic polymers have, for the most part, replaced naturally occurring materials such as animal glues, starches and vegetable gums in many adhesive applications. The key to this replacement was the development and use of tackifier resins in the formulation with synthetic polymers, because they give the system the ability to wet the substrate surface and thus form a strong bond. Without tackifiers in the adhesive formulation, the synthetic polymers have low tack and peel adhesive performance.
Various resinous materials have been suggested as tackifiers for synthetic polymers. Examples of materials suggested include rosin, disproportionated rosin, rosin esters such as glycerol esters of rosin and pentaerythritol esters of rosin, aliphatic hydrocarbon resins from petroleum, aromatic petroleum resins, dicyclopentadiene (DCPD) resins, terpene resins, terpent/phenol resins and cumarone/indene resins.
Tackifiers are resins that can be considered as high viscosity solvents for the base polymer. The term tackifier therefore, cannot be given to any material unless we relate that material to the product that it tackifies.
Acrylic polymer compositions have long been used as adhesive compositions, particularly in pressure sensitive adhesive (PSA) compositions. Common PSA compositions include a high-molecular-weight acrylic base polymer and a tackifying resin and when required, plasticizer, stabilizer, antioxidant, filler, coloring agent and the like. PSA compositions should have a high initial tack so that the adhesive surface merely needs to be contacted and pressed to the surface to achieve bonding. There should be little or no requirement to hold the adhesive and substrate in position for any significant time while a bond develops.
In developing adhesive formulations one seeks the optimum combination of several adhesive properties and since it is not generally possible to achieve the optimum for every property it is necessary to obtain the best balance of properties for the particular use in mind. In e.g. PSA compositions which are used in the label industry one tries to optimise the loop tack and peel and at the same time provide an adhesive whose component will not migrate during storage.
Nowadays mainly rosin derivatives, such as disproportionated rosin acids, and hydrocarbon resins are commercially used as tackifiers for adhesive compositions comprising acrylic polymers. The rosin derivatives have been preferred due to better compatibility with acrylics.
Initially most important were the solvent acrylics, but environmental, health and safety needs of industry have resulted in dramatic growth in water borne adhesive compositions comprising acrylic polymers. With increasing desirability of water borne systems and often their demonstration of significant performance enhancements with tackifier resins, new tackifier resins suitable for these systems are being sought.
U.S. Pat. No. 5,120,781 discloses tackifiers for hot melt adhesive compositions. The tackifiers are produced by reacting rosin and a polyhydric alcohol under conditions effective to substantially complete the esterification reaction. The resulting reaction product is then reacted with an aromatic dibasic acid providing a tackifier with a content of rosin above 78 weight %.
U.S. Pat. No. 4,981,939 refers to a binder for preparing toners which are used for developing electrostatic images formed in the process of electrography. The toner comprises as the main component a polyester composed of a polybasic acid component and a polyhydric alcohol component and a rosin modified polyhydric alcohol. The rosin modified polyhydric alcohol is produced by reacting a polyhydric alcohol having three or more hydroxyl groups with a rosin resulting in a polyester network (cross-linking).
WO 9942508 relates to low viscosity aromatic polyester polyols prepared by reacting a phthalic acid based material with diethylene glycol, a higher functional polyol having an average functionality of greater than two and a long chain alkyl acid, ester or oil. The resulting aromatic polyester polyol is a branched polyester.
U.S. 3,438,918 refers to rubber compositions obtained by reacting polyhydric alcohols, polybasic acids and oils.
Thus one advantage of the present invention is to provide a tackifier which is compatible with water borne pressure sensitive adhesive compositions and hot melt pressure sensitive adhesive compositions.
The further advantage with the present invention is the improvement of overall adhesive properties of adhesive compositions and specifically improving the properties of loop tack and peel and at the same time provide an adhesive (composition) whos component(s) will not migrate during storage.
A still further advantage with the present invention is to provide a polyester tackifier comprising a minimum amount of rosin derived from natural sources thereby reducing the cost of production, i.e. a polyester which is capped at both ends with a monofunctional compound (a polyester containing not more than two rosin residues).
Another advantage with the present invention is to provide a straight chain polyester resin being solid or liquid.
Still further advantages of the present invention are disclosed by the following specification.
The present invention relates to a polyester tackifier and a pressure sensitive adhesive composition comprising the polyester tackifier according to the claims. More specifically, the present invention relates to a polyester tackifier which is obtainable by polymerising a mixture comprising a diacid or derivative thereof, a diol, and at least 6 molar % of an organic monofunctional compound, wherein the mixture is essentially free from compounds comprising more than two carboxylic acid groups or alcohol groups and a pressure sensitive adhesive composition comprising said polyester tackifier. The present invention also relates to the use of the polyester tackifier, an aqueous pressure sensitive adhesive composition, a hot melt pressure sensitive adhesive composition and a method for manufacturing a polyester tackifier.
The polyester tackifier is suitably obtained by esterification of at least one diacid or derivative thereof, at least one diol, and at least 6 molar % of an organic monofunctional compound, wherein the mixture is essentially free from compounds comprising more than two carboxylic acid groups or alcohol groups, i.e. suitably essentially free from compounds comprising more than two functional groups enabling the compounds of taking part in the polymeric esterification reaction. The diols and diacids preferably will produce an alternating linear/non-branched condensation polymer which is terminated at both ends by the organic monofunctional compound, the latter functioning as a chain stopper, i.e. capper.
The diacids which can be used in the present invention are organic diacids such as organic dicarboxylic acids or derivatives thereof. By derivatives thereof is meant acid anhydrides or any other acid capable of forming an ester moiety in the polyester. Suitably, the dicarboxylic acids are aliphatic, cyclic or aromatic, whereby aromatic dicarboxylic acids or derivatives thereof are preferred. Even more preferred are aromatic dicarboxylic acids having the dicarboxylic acid moieties in para or ortho position such as terephthalic acid and phthalic acid. Aromatic dicarboxylic acids having the diacid moiety in the ortho position are especially favourable such as phthalic acid. The aliphatic diacids can be branched or linear comprising from 4 up to 12 carbon atoms. The term diacids also encompasses acid anhydrides where appropriate as well as chlorides and esters of carboxylic acids. Examples of useful diacids are selected from the group comprising terephthalic acid, isophthalic acid, phthalic acid, malonic acid, dimethyl malonic acid, succinic acid, glutaric acid, adipic acid, trimethyladipic acid, pimelic acid, 2,2-dimethylglutaric acid, azelaic acid, sebacic acid, fumaric acid, maleic acid, itaconic acid, pimelic acid, 1,3-cyclopentanedicarboxylic acid, 1,2 cyclohexanedicarboxylic acid, 1,4-cyclohexanedicarboxylic acid, 2,5 norbornanedicarboxylic acid, 1,4 naphthalic acid, diphenic acid, 4,4xe2x80x2-oxydibenzoicacid, diglycolic acid, 2,5-naphtalenedicarboxylic acid and/or mixtures thereof.
The diols, often also referred to as glycols, used in the present invention are preferably linear or branched aliphatic diols, cyclic diols, aromatic diols, alkylene glycols or polyalkylene glycols or mixtures thereof, whereby alkylene glycols or polyalkylene glycols or mixtures thereof are especially preferred. Specific polyalkylene glycols may be polyethylene glycol and polypropylene glycol notably having from 1 up to 4 repeating alkylene oxide units, more preferably from 2 up to 3 repeating units. The polyoxyalkylene glycols may comprise both ethylene oxide and propylene oxide unit. Suitable diols are selected from the group of ethylene glycol, propylene glycol, diethylene glycol, triethylene glycol, tetraethylene glycol and dipropylene glycol or mixtures thereof. Other suitable diols can be selected from the group of 1,3-propanediol, 1,3-butanediol, 1,4-butanediol, 1,5-pentanediol, 1,6-hexanediol, 1,7-heptanediol, 1,8-octanediol, 1,9-nonanediol, 1,10-decanediol, 2-methyl-1,3-propanediol, 2,4-dimethyl-2-ethylhexane-1,3-diol, 2,2-dimethyl-1,3-propanediol, 2-ethyl-2-butyl-1,3-propanediol, 2-ethyl-2-isobutyl-1,3-propanediol, 3-methyl-1,5-pentanediol, 2,2,4-trimethyl-1,6-hexanediol, 1,2-cyclohexanedimethanol, 1,3-cyclohexanedimethanol, 1,4-cyclohexanedimethanol, 2,2,4,4-tetramethyl-1,3-cyclobutanediol, 4,4xe2x80x2-methylenediphenol, 4,4xe2x80x2-(2-norbornyliden)-diphenol, 4,4xe2x80x2-dihydroxybiphenol, o-, m-, p-dihydroxybenzene, 4,4xe2x80x2-isopropylidenediphenol, 2,5-naphtalenediol, p-xylenediol, cyclopentane-1,2-diol, cyclohexane-1,2-diol, cyclohexane-1,4-diol, etherified diphenols such as bisphenol A-alkylene oxide adducts and/or mixtures thereof.
The organic monofunctional compounds used in the present invention are suitably monocarboxylic acids or monohydric alcohols. Preferably, the organic monofunctional compounds are monocarboxylic acids exemplified by rosins (colophonies) derived from natural sources such as gum rosins, wood rosins and tall-oil rosins. These naturally occurring rosins are suitably mixtures and/or isomers of monocarboxylic tricyclic rosin acids usually containing 20 carbon atoms. The tricyclic rosin acids differ mainly in the position of the double bonds. Typically the rosin is a mixture of substances comprising levopimaric acid, neoabietic acid, palustric acid, abietic acid, dehydroabietic acid, seco-dehydroabietic acid, tetrahydroabietic acid, dihydroabietic acid, pimaric acid, and isopimaric acid. The rosins derived from natural sources also include rosins, i.e. rosin mixtures, modified notably by polymerisation, isomerisation, disproportionation and hydrogenation. Furthermore, the rosins may be treated with an aldehyde, for example formaldehyde, giving a rosin alcohol. Apart from rosins, carboxylic acids, such as naphtenic acid, and carboxylic acid or alcohol functionalised petroleum resins (aliphatic and/or aromatic) can be used. The mixture comprises suitably at least 10 molar % of the organic monofunctional compound, preferably, at least 15 molar %.
The polyester tackifier is suitably prepared by polymerising a mixture comprising from 15 up to 45 molar %, based on total monomers, more preferably from 20 up to 40 molar % and most preferably from 30 up to 35 molar % of a diacid, from 30 up to 55 molar %, based on total monomers, more preferably from 40 up to 55 molar % and most preferably from 45 up to 50 molar % of a diol, and from 6 up to 40 molar %, based on total monomer, more preferably from 10 up to 40 molar % and most preferably from 15 up to 35 molar % of a monofunctional compound, wherein the mixture is essentially free from compounds comprising more than two carboxylic acid groups or alcohol groups. Suitably, the mixture is essentially free from any compound comprising more than two functionalities which can take part in the polymerisation reaction, i.e. compounds comprising more than two functionalities or derivatives thereof which can be contained in the polyester tackifier. By essentially free is usually meant that the mixture comprises less than 5 molar %, preferably less than 1 molar %, most preferably less than 0.1 molar %, based on total monomers, of compounds comprising more than two carboxylic acid groups or alcohol groups. Thus, the polyester tackifier is suitably a non-branched polyester. In case where an excess of diol over diacid is present in the monomer mixture, a monocarboxylic acid usually is employed as chain stopper to xe2x80x9ccapxe2x80x9d the polyester whereby a monocarboxylic acid (rosin) terminated polyester is obtained. In the reversed situation, excess diacid over diol present in the monomer mixture, a monohydric alcohol can be employed as chain terminator to cap the polyester.
The polyester tackifier of the present invention is suitably formed by a condensation polymerisation (esterification) carried out in an inert gas atmosphere. Furthermore, the condensation reaction may be conducted in the presence of catalytical amounts of at least one esterification catalyst. Usually esterification catalysts include phosphoric acid, phosphorous acid, hypophosphorous acid, para-toluene sulfonic acid, lithium carbonate, calcium hydroxide, zinc oxide or mixtures thereof. Additionally, a disproportionation catalyst may be present if one or more rosins are employed. Examples of disproportionation catalyst can be supported or non-supported metals such as palladium, nickel and platinum and furthermore iodine, iodides, sulfides, mono- and poly phenol sulfides (i.e. amylophenol sulfide polymer). The esterification catalyst is generally present in amounts between about 0.01 and 0.1 weight %, notably between 0.05 and 0.07 weight %; while the disproportionation catalyst usually is present in amounts between about 0.1 and 0.3%, all being weight percents based on the weight of total monomers. In those embodiments utilising esterification and/or disproportionation catalysts, the catalyst is suitably added after the building blocks have been molten.
The monomer mixture is generally polymerised at a temperature ranging from 150xc2x0 C. up to 350xc2x0 C., usually from 220xc2x0 C. up to 280xc2x0 C., and most preferably from 250xc2x0 C. up to 260xc2x0 C. until distillation of water has ceased. Typically the reaction time may vary from 10 up to 30 hour, more preferably from 12 up to 20 hour, and most preferably from 14 up to 16 hours. The reaction usually is terminated when the acid value has dropped below 25 mg KOH/g and/or the acid value change has dropped below 1 mg KOH/g/hour.
The polyester resins according to the invention preferably have number average molecular weight (Mn) between 400 and 6000, more preferably between 400 and 2000, and most preferably between 500 and 1800. The molecular weight distribution of the resins, measured by the polydispersity index generally ranges from 1.1 up to 2.0 and more preferably from 1.1 up to 1.3.
The physical state of the polyester resin can be solid or liquid at ambient temperature depending on reaction conditions and monomers used, specifically which type of diols are used. The novel polyester resins are suitably blended with other tackifiers such as pentaerythritol esters of rosin.
The present invention also refers to pressure sensitive adhesive compositions comprising a polymer and the polyester tackifier described above. Pressure sensitive adhesive compositions comprising the polyester tackifier described above are especially advantageous for low temperature applications such as giving good adhesive properties when used at temperatures well below 0xc2x0 C. In addition, adhesive compositions can be produced at lower cost with corresponding or improved tackifier properties when all or part of the conventional tackifiers, e.g. tackifiers based on pentaerythritol, are substituted by the above defined novel polyester tackifier.
The present invention furthermore refers to the use of the tackifier for pressure sensitive compositions.
According to one preferred embodiment of the present invention the polyester tackifier is comprised in aqueous pressure sensitive adhesive (PSA) compositions further containing other polymers.
The tackifier is preferably supplied in form of an aqueous dispersion. The tackifier is dispersed in water using dispersing agents such as ethoxylated phosphate ester surfactants. The amount of dispersing agent used is usually from 2 up to 6 weight % based on tackifier. The polyester tackifier is suitably present in the aqueous tackifier dispersion in an amount from 40 up to 65 weight % based on total tackifier dispersion, more preferably from 50 up to 57 weight %.
The pressure sensitive adhesive compositions and the aqueous adhesive compositions according to the present invention comprise polymers. Suitable polymers are exemplified by natural and synthetic rubbers such as polychloroprene rubber, styrene-butadiene rubbers, SIS block copolymers, styrene butadiene styrene (SBS) block copolymers, VAE (vinylacetate ethylene copolymers), nitrile rubbers and polyisobutylene rubbers, acrylate polymers, acrylic polymers such as acrylic esters and methacrylate polymers or mixtures thereof.
Especially suitable polymers used in aqueous adhesive compositions according to the invention are acrylic polymers and/or acrylic ester copolymers dispersed in an aqueous phase which can be obtained by emulsion polymerisation of a wide range of olefins and acrylates such as 2-ethylhexyl acrylate and butyl acrylate. The polymer is suitably present in the form of an aqueous polymer dispersion in an amount from 50 up to 70 weight % based on total polymer dispersion, preferably from 55 up to 65 weight %.
The aqueous adhesive composition usually comprises the tackifier dispersion in an amount from 10 up to 40 weight % based on total aqueous composition, preferably from 20 up to 30 weight %, and the polymer dispersion in an amount from 60 up to 90 weight % based on total aqueous composition, preferably from 70 up to 80 weight %.
Other compounds known to the person skilled in the art may also be comprised in the water borne adhesive composition exemplified by plasticisers, stabilisers, antioxidants, fillers, colouring agent and the like.
According to a further preferred embodiment, the polyester resin tackifier is comprised in a hot melt pressure sensitive adhesive (PSA) composition. Accordingly, the present invention encompasses hot melt pressure sensitive adhesive composition comprising the above defined polyester tackifier. The hot melt compositions, preferably contains polymer resins including ethylenic copolymers of ethylene and other various monomers such as vinyl acetate, methyl acrylate, ethyl acrylate and other acrylates. In addition, styrenic block copolymers (SBC), such as styrene-butadiene-styrene (SBS), styrene-isoprene-styrene (SIS) and styrene-ethylene-butylene-styrene (SEBS) are employed in the present invention. Ethylene/vinyl acetate (EVA) and SBS polymers are particularly preferred.
In addition, ethylenic copolymer-based hot melt compositions may comprise mineral waxes such as paraffin wax and microcrystalline wax and synthetic waxes such as polyethylene wax and polypropylene wax. Other animal or vegetable waxes may also be used.
Preferred examples of oil used in the SBC-based hot melt compositions of the present invention include mineral oils of relatively high molecular weight and olefin oligomers. Other vegetable and/or animal oils may be used.
The polyester tackifier is preferably added to the hot melt composition from 10 up to 60% by weight based on total composition more preferably from 30 up to 60% by weight.
The styrenic block copolymers are suitably added from 10 up to 75% by weight more preferably from 10 up to 40% by weight.
The wax may be added from 5 up to 50% by weight, suitably from 5 up to 30% by weight.
The amount of polymers/copolymers and other compounds contained in the adhesive compositions, i.e. aqueous compositions or hot melt compositions, is/are not critical and may vary so as to give the preferred properties of the adhesive composition. The compounds can be in any physical state guided by the state of the adhesive composition such as dispersed in an aqueous phase, liquid or solid.
The invention is further illustrated by the following examples, which, however, are not intended to limit the same. All units (parts or percentages) are by weight unless otherwise indicated.